The invention relates to a process for starting an internal-combustion engine. The invention further relates to an internal-combustion engine having a starting-aid device.
Internal-combustion engines (such as Otto and Diesel engines) are less inclined to start at lower temperatures. In order to ensure a robust start of the internal-combustion engine, excessively increased quantities of fuel, among other things, are fed (“lubricating”). Major amounts of undesirable pollutants, such as smoke particulates and HC (hydrocarbons) are therefore generated during a cold-starting operation. In most relevant emission cycles, the internal-combustion engine is to be cold-started at least once. The emissions produced during the brief cold-starting operation correspond to a considerable fraction of what the internal-combustion engine emits as harmful exhaust gases during the entire emission cycle. It is therefore a challenge to developers of internal-combustion engines to, on the one hand, ensure the cold-starting capability of the internal-combustion engine and, on the other hand, minimize undesirable pollutants during the starting operation. Furthermore, start-stop systems for internal-combustion engines are increasingly used for improving energy efficiency. These start-stop systems require a starting of the internal-combustion engine that is as fast as possible.
As a rule, internal-combustion engines have an electric starter motor (“starter”) that is coupled by way of a wheel gear or belt gear and has an output just sufficient for securely starting the internal-combustion engine. Here, the dimensioning, on the one hand, is a result of the cost of the starter and, on the other hand, is limited by the available power from the current source (vehicle battery). This is illustrated in FIG. 1 by a diagram of a course of a speed n over the time t during the start of an internal-combustion engine according to the state of the art. A firing speed or starting speed na of the internal-combustion engine is therefore always below its idling speedz, which necessitates a start of the combustion operation below the stable speed limit that is defined by the idling speed nz. In a starting device operation AV1, the starter will drive the internal-combustion engine until it reaches the starting speed na. Then, an ignitable fuel-air mixture will be ignited at a point in time t1 (in the case of an Otto engine, by applied ignition; in the case of a Diesel engine, by self-ignition), which is indicated by a lightning symbol. For this purpose, this fuel-air mixture may also only be injected into the combustion chamber when the starting speed na has been reached. After that, the combustion will start. The starter is switched off beforehand, and the speed n of the internal-combustion engine decreases again to a point in time t2, until the internal-combustion engine or the engine is accelerated by means of the combustion energy in an internal-combustion engine operation VM1 to the set idling speed nz and reaches a stable course at the point in time t3.
During a cold starting operation, the maximal air or mixture temperature in the cylinder (combustion chamber) will fall because of the low ambient temperature. Particularly in the case of Diesel engines, it can happen that the self-ignition temperature of the fuel is not reached at the end of the compression stroke. As a result the engine possibly cannot be started at all at the starting speed na. Typical measures for increasing the cold-starting capability are the reduction of leakages and losses of heat, the increase of the injected or fed fuel quantity as well as diverse systems for the starting aid of the combustion engine or of the internal-combustion engine, such as a heater plug (“preheating”). However, this measure for improving the starting capability will simultaneously lead to an emission problem. The reason is that, as a result of the high quantity of fuel and the low temperature, the combustion takes place in an incomplete manner. This has the result that many particulates and hydrocarbons occur as products of the incomplete combustion. When the air ratio (^,lambda) falls below the so-called soot limit (at ^≈1.2), the particulate emission will rise superproportionally.
In addition, several systems exist for a pneumatic starting aid of an internal-combustion engine by means of compressed air. In one case, the compressed air can drive the turbine of a pneumatic starter motor. In another case, the compressed air can be introduced directly into one or more cylinders during the power cycle in order to pneumatically accelerate the crankshaft. For example, several industrial-scale Diesel engines (such as marine diesel engines or stationary systems for generating emergency power) have a pneumatic starting system consisting of an air compressing device, a compressed-air reservoir, a pneumatic distributor and starter valves. The compressed air generated by an air compressor is stored in one or more compressed-air reservoirs provided for the pneumatic starter. The pneumatic distributor will then take over the task of distributing the compressed air from the compressed-air reservoir to the respective starter valves in the cylinder head of the internal-combustion engine. By way of the starter valves, the compressed air is admitted into the cylinders in order to drive the respective pistons from the top dead center in a downward motion (while the pistons are upright) to the bottom dead center. During the subsequent upward motion of the respective piston, the expanded air is discharged through the normal exhaust valves. The acceleration of the crankshaft takes place purely pneumatically up to the ignition of the engine.
In the case of hybridized vehicles having an additional driving system, a starter (starter motor) is no longer necessary. An electric motor in the hybrid drive train takes over the starting aid for the combustion engine. In addition, the higher-power electric motor is capable of accelerating the combustion engine directly up to its idling speed.
International Patent Document WO-2006/089779 describes a device which takes compressed air from the compressed-air system of a vehicle and briefly blows it into the fresh-air supply system of a piston combustion engine with turbocharging in order to avoid the so-called “turbo-lag”. This so-called “pneumatic booster system” (PBS) forms a device for a process for improving the accelerating performance of the piston internal-combustion engine with turbocharging.
It is therefore an object of the present invention to provide an improved process for starting an internal-combustion engine.
A further object consists of creating an internal-combustion engine having a starting-aid device.
According to one aspect of the invention, additional air from an inlet gas supply device, which is provided for a brief blowing-in of air for eliminating the so-called turbo-lag, is blown into the intake pipe when starting the internal-combustion engine.
Accordingly, a process for starting an internal-combustion engine, particularly a Diesel engine, having an exhaust gas turbocharger and an inlet gas supply device having at least one compressed-air reservoir, which is connected with an intake pipe of the internal-combustion engine, is provided, whereby, during the starting of the internal-combustion engine, additional air is blown from the inlet gas supply device into the intake pipe until a speed of the internal-combustion engine reaches a previously definable idling speed.
Such a starting aid formed by the so-called pneumatic booster system additionally provides the internal-combustion engine with the advantages of improving the cold-starting capability for the inner-engine emission reduction and also for implementing a start-stop function.
The already existing infrastructure of the PBS system can be utilized for efficiently and rapidly starting the internal-combustion engine while its emissions are low. By means of an electronic control and an intelligent communication with the engine system, various processes ranging from a pneumatic starting aid to a purely pneumatic start can be implemented by means of the PBS.
This can be provided in a first embodiment in that the following process steps are carried out:
(S1) Driving the internal-combustion engine in a starting device operation by means of an electric starter until the internal-combustion engine reaches a starting speed;
(S2) igniting the fed ignitable fuel-air mixture when the starting speed is reached; and
(S3) blowing in additional air from the inlet gas supply device and increasing the speed of the internal-combustion engine in an internal-combustion engine operation until a speed of the internal-combustion engine reaches a previously definable idling speed.
After the igniting, the internal-combustion engine is acted upon by the additional air, whereby, despite a high injection quantity of fuel, as a result of the additional air, the air ratio reaches a clearly higher value than in the state of the art. Hydrocarbon and particulate emissions are thereby lowered.
In a second embodiment, it is provided that the following process steps are carried out:
(S1) Driving the internal-combustion engine by means of an electric starter in a first starting device operation until the internal-combustion engine reaches a previously definable intermediate speed;
(S2) driving the internal-combustion engine by blowing in additional air from the inlet gas supply device and increasing the speed of the internal-combustion engine in a second starting device operation until a speed of the internal-combustion engine reaches a previously definable idling speed; and
(S3) igniting a fed ignitable fuel-air mixture when the previously definable idling speed is reached.
No fuel is injected during the pneumatic start. The internal-combustion engine is accelerated to the idling speed; only then will the ignition take place. The “dirty starting phase” is completely bypassed. No harmful exhaust gases are generated in the process.
The following process steps are carried out in a third embodiment:
(S1) Driving the internal-combustion engine in a starting device operation by blowing in additional air from the inlet gas supply device and increasing the speed of the internal-combustion engine until a speed of the internal-combustion engine reaches a previously definable idling speed; and
(S2) igniting a fed ignitable fuel-air mixture when the previously definable idling speed is reached.
In this case, the PBS system, which is present anyhow, is utilized as an electronically controlled additional air system, in which case the required infrastructure is available free of charge and can isochronously intelligently (for example, by a CAN bus linkage) in a simple manner be linked with the engine timing gear. In this case, only a variable valve gear is still required which is also already present in many cases. Additional components for generating and controlling the compressed air are eliminated because they are also already present. The PBS system is used for the pneumatic engine start and the starting aid respectively as well as for improving the transient performance.
As a result, during the blowing-in of additional air from the inlet gas supply device, a negative valve overlap of the valves of the internal-combustion engine can be adjusted by the variable valve gear. As a result, it is prevented that the blown-in additional air escapes to a certain extent.
In a further development, it is provided that, after the previously definable idling speed has been reached, the blowing-in of additional air from the inlet gas supply device can be adjusted after a previously definable time segment. In addition, the volume of the blown-in additional air can be adjusted by the inlet gas supply device. Thus, in the intake phase, at the idling speed or the increased idling speed.
During the blowing-in of additional air from the inlet gas supply device, a flap is closed in order to prevent a return flow of the additional air into a compressor of the exhaust gas turbocharger. As a result, losses of pressure and volume of the additional air can be further reduced.
It is also provided that, at predefinable points in time and/or when its aid is required, the electric starter can be switched on. A further aid function is thereby provided. The starter may also be available as an emergency starter when, for example, no or no sufficient compressed air is available.
An internal-combustion engine, particularly a Diesel engine, having an exhaust gas turbocharger comprises an inlet gas supply device in an intake pipe of the internal-combustion engine; a compressed-air system having at least one compressed-air reservoir that can be connected with the inlet gas supply device; an engine timing gear and a starting-aid device having a control device, the starting-aid device being constructed for controlling the inlet gas supply device for blowing in additional air when starting the internal-combustion engine for implementing a process for starting an internal-combustion engine. This process may be the above-described process.
The starting-aid device comprises a control device which, as software, is a component of the engine timing gear. This results in no additional space requirement.
In an alternative embodiment, the starting-aid device may have a separate control device that is connected with the engine timing gear. Advantageously, retrofitting of existing installations is therefore also possible.
In another embodiment, it is contemplated for the engine timing gear to be constructed for a start-stop operation of the internal-combustion engine. The advantages of the starting-aid device and of the above-described process can therefore be used extensively.
This can be implemented, for example, in that the engine timing gear communicates with a control of the inlet gas supply device, the control device of the starting-aid device and with a clutch/transmission control for implementing the start-stop operation of the internal-combustion engine by way of an electric interface. The electric interface may, for example, be an interface of a bus system, such as a CAN bus.
The advantages and potential for cold, as well as also warm, starting processes resulting from the above-described process and the above-described internal-combustion engine are the following:
(1) Improvement of the (cold) starting capability of internal-combustion engines per se.
(2) Reduction of costs of an electric starter because it can have a smaller design for extreme starting situations.
(3) Reduction of emissions during the starting operation; thereby in turn                (a) reduction of the extent of the exhaust gas aftertreatment,        (b) observing of tightened transient exhaust gas regulations.        
(4) Reduction of the fuel consumption during the starting operation.
(5) Acceleration of the starting operation, thereby in turn                (a) making a start-stop system possible.        
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.